Diabetes mellitus is a group of clinical syndromes induced by the genetic and environmental interactions, and involves a series of metabolic disorders in carbohydrate, protein, fat, water, electrolyte, etc. due to absolute or relative deficiencies in insulin secretion and reduced insulin sensitivity of the target tissue cells. Clinically, diabetes mellitus is mainly characterized by hyperglycemia, and may lead to various complications, such as blindness, cardiovascular diseases, kidney damage, and the like, as time goes on, and acute metabolic disorders such as ketoacidosis etc. may occur in serious conditions and stress. Therefore, diabetes mellitus and complications thereof have been worldwide public health problems that severely threaten human health.
Diabetes mellitus is mainly classified into two types, namely type I diabetes mellitus (insulin-dependent diabetes mellitus, IDDM) and type II diabetes mellitus (non-insulin-dependent diabetes mellitus, NIDDM). Type I diabetic patients have abnormal response to stimuli of environmental factors due to genetic susceptibility determined by HLA-D gene in the short arm of chromosome 6, which leads to the destruction of the pancreatic beta-cells through autoimmune response, and thus the insulin is absolutely deficient. Hence, the type I patients have to rely on insulin therapy to maintain their lives. The type II diabetes mellitus which accounts for 90% or more in the diabetic patients is caused by the relative deficiencies in insulin secretion and/or insulin resistance. Type II diabetes mellitus is also strongly affected by genetic factors, and shows significant heterogeneity, that is, its pathogenesis is varied and complicated, and there are great differences among type II diabetic patients.
Type II diabetes mellitus is accompanying with the decrease in insulin sensitivity of tissues sensitive to insulin, i.e. insulin resistance, which is because the insulin signal is weakened or disordered during the transduction, resulting the impaired glucolipids metabolism in muscle, liver and adipose tissues. During the signal transduction in the insulin signaling pathway, the insulin secreted into body fluid binds with the insulin receptor (IR) subunits of the cells sensitive to insulin first. After IRs form dimers, the subunits phosphorylate the tyrosines at the active sites by auto-phosphorylation, thus activating the protein tyrosine kinase (PTK) of the IR subunits. Then adapter proteins containing SH2 domain, such as insulin receptor substrate (IRS) 1-4, are recruited to the SH2 binding sites of the IR, and PI3Ks are activated. After that, the PKBs and GLUT4s in the downstream glucose metabolism pathway are further activated, and the glucolipids metabolism in body is initialized. During the signal transduction, an important regulating mechanism is the reversible regulation of the protein tyrosine phosphorylation of IR, IRS and other downstream molecules (White M. F., Kahn C. R.; J. Bio. Chem., 1996, 269, 1-4): the activated phosphorylated IRs are internalized, migrated to endoplasmic reticulum and de-phosphorylated by a specific tyrosine phosphatase (PTPase) such as PTP1B to lose their activity, thus terminating the insulin signal. Therefore, it can be seen that, the impaired enzyme activity between the specific PTPases and the PTKs in insulin pathway may be the reason to cause the insulin resistance of the type II diabetes mellitus. Thus, it has been a more and more important approach for treating type II diabetes mellitus by inhibiting the activity of PTPases through searching an inhibitor which selectively acts on the PTPases in the pathway to enhance and prolong the insulin signal.
PTPases include a large family of transmembrane receptor and intracellular non-receptor type enzymes. The intracellular protein tyrosine phosphatase 1B (PTP1B) is one of PTPases that is first purified and determined the biological properties. It is about 50 kDa in length, and has a cutable hydrophobic segment with 35 amino acids at its C end. The segment is responsible for locating PTP1Bs in endoplasmic reticulum (Frangioni J. V., Beahm P. H., Shifrin V., et al.; Cell, 1992, 68, 544-560). The PTP1Bs located in endoplasmic reticulum are dephosphorylated by interacting with receptor type kinases such as IR, EGFR (epidermal growth factor receptor) and PDGFR (platelet-derived growth factor receptor) (Boute N., Boubekeur S., Lacasa D., et al.; EMBO Rep., 2003, 4(3), 313-319; Haj F. G., Verveer P. J., Squire A., et al.; Science, 2002, 295(5560), 1708-1711).
Experimental results show that PTP1B plays a key role in negatively regulating the kinase activity of IR and the phosphorylation level of IRS (Johnson T. O., Ermolieff J., Jirouesk M. R.; Nat. Rev. Drug disc., 2002, 1(9), 696-709). PTP1B is generally expressed in the tissues sensitive to insulin, and its protein expression and phosphatase activity are higher in the skeletal muscles and adipocytes of abetic peoples and rodent animals suffering insulin resistance than in control group, which shows that the improved PTP may have an important function during the pathological process of insulin resistance (Ahmad F., Azevedo J. L., Cortright R., et al.; J. Clin. Invest., 1997, 100(2), 449-458; Ahmad F., Considine R. V., Bauer T. L., et al.; Metabolism, 1997, 46(10), 1140-1145). The high expression of PTP1B in L6 muscle cells and Fao cells by adenovirus-mediated gene transfection, can significantly suppress the phosphorylation levels of IR and IRS-1 which are induced by insulin, thereby inhibiting the transduction of the downstream pathway thereof and the final glyconeogenesis (Egawa K. et al.; J. Biol. Chem., 276(13), 10207-10211). By treating rat hepatocytes KRC-7 with a specific neutralizing antibody of PTP1B, Ahmad et al. found that the sensitivity of the insulin signaling pathway could be improved by inhibiting the activity of intracellular PTP1B with the antibody, and the phosphorylation levels of IR and IRS-1 and the PI3K activity of the downstream pathway thereof can also be increased apparently (Ahmad F., et al.; J. Biol. Chem., 1995, 170(35), 20503-20508).
A more important experimental evidence comes from PTP1B knockout mice. It is reported by Elchebly et al. that the PTP knockout mice produced by homologous recombination can maintain their normal physiological conditions, and have significantly enhanced insulin sensitivity, which are related to the enhanced phosphorylation levels of IR and IRS-1 in liver and skeletal muscle (Elchebly M., et al.; Science, 283, 1544-1548). Surprisingly, PTP1B knockout mice are also capable to a certain extent of resisting the weight gain and insulin resistance induced by food, which is because the adipocyte volume decreases without varying the amount of the adipocytes and the in vivo energy metabolism rate increases (Klaman L. D., et al. Mol. Cell. Bio., 20(15), 5479-5489). These prove the important roles of PTP1B in insulin sensitivity, energy consumption and fat storage.
There are increasing genetic evidences showing that PTP1B is related to insulin resistance, obesity, type II diabetes, and the like, with the progress in Human Genome Project. The human protein tyrosine phosphatase 1B (hPTP1B) gene is located in 20q13.1-13.2 of human chromosome, and has 10 exons with two splicing forms, wherein one contains only the previous 9 exons and the other includes all the 10 exons. Both expressions of the two forms are regulated by the insulin signal itself (Forsell P. A., Boie Y., Montalibet T., et al.; Gene, 2003, 260(1-2), 145-153). It was found that the insulin sensitivity of retinal adipose tissue decreased when PTP1B was over-expressed and had excessive activity in the tissue, resulting in insulin resistance in the whole body (Wu X. D., et al.; J. Clin. Endocrinol Metab, 2001, 86, 5973-5980). It is found that a inserional mutation in some people can improve the stability of PTP1B mRNA, and thus increase the expression level of PTP 1 B, while it is often accompanied with insulin resistance and the increase of triglyceride and high-density lipoprotein (HDL) in these people (Echwald S. M., et al.; Diabetes, 2002, 51, 1-6). In addition, a rare Pro387/Leu mutation was found and it can prevent Ser in the PTP1B regulating sequence from being phosphorylated, and result in a relatively high enzyme activity of PTP1B on average. The probability of these people to suffer type II diabetes is 3.7 folds higher than that of normal people (Echwald S. M., et al.; Diabetes, 2002, 51, 1-6). Single nucleotide polymorphism (SNP) of 981T/981C located in exon No. 8 was found in OJI-OREE people, while the risk of these people to suffer type II diabetes and impaired glucose tolerance (IGT) is 42% lower than that of normal people, which is due to the relatively low enzyme activity of PTP1B on average (Di Paoia R., et al.; Am. J. Hum. Genet., 2002, 70, 806-812).
In summary, PTP1B is a novel potential target for treating diabetes and obesity. The therapeutic effect for diabetes and obesity will be greatly improved by repressing the PTP1B activity in the tissues sensitive to insulin. Therefore, it has a wide application prospect for selecting a specific inhibitor against PTP1B.
Some progresses have been made in the study on the selective inhibitors against PTP1B. However, most of the selective inhibitors are limited to some peptide or peptoid compounds, such as EEDE(F2PMP)M (Ki=7.2 nM) and Glu-F2PMP-F2PMP (IC50=40 nM) which are inhibitors designed based on the sequence of the de-phosphorylating substrate of PTP1B. It is hard for these peptide inhibitors to be drugs due to the fact that they are peptide phosphate compounds, although they have a relatively strong inhibiting activity and a relatively high selectivity. Recently, a series of PTP1B inhibitors which are non-peptide non-phosphate compounds were reported that they have certain selectivity. More importantly, some of the compounds have significant activity on reducing the glucose and insulin levels in the blood plasma of ob/ob mice. This is the first direct evidence in pharmacology showing that PTP inhibitors have an activity for treating diabetes (Malamas, M. S., et al. J. Med. Chem., 2000, 43, 1293-1310). These results provide a potential without doubt to find novel small molecular non-peptide organic compounds to be used as PTP1B inhibitors with high activity and selectivity.